1. Field of the Invention
The present invention relates to a novel crystalline trehalose dihydrate, its process and uses, and more particularly to a novel crystalline trehalose dihydrate which has an elongated crystalline structure with a proportion of the length in the c axis to that in the b axis less than 2.0, its process and uses as compositions containing the crystal.
2. Description of the Prior Art
Trehalose or xcex1,xcex1-trehalose has been long known as a non-reducing saccharide composed of D-glucose units. As described in Advances in Carbobydrate Chemistry, Vol. 18, pp. 201-225 (1963), published by Academic Press, USA, and Applied and Environmental Microbiology, Vol. 56, pp. 3,213-3,215 (1990), trehalose widely exists in microorganisms, mushrooms, insects, etc., though the content is relatively low. Since non-reducing saccharides including trehalose do not react with amino-group-containing substances such as amino acids and proteins, they neither induce amino-carbonyl reaction nor deteriorate amino-acid-containing substances. Thus, the non-reducing saccharides have been recognized to be processed without fear of causing undesirable browning and deterioration, and their mass-productions have been in great demand.
Industrial-scale production of crystalline trehalose dihydrate has been realized, for example, by using in combination several enzymes, in particular, a non-reducing saccharide-forming enzyme, as disclosed in Japanese Patent Kokai No. 143,876/95, which forms a non-reducing saccharide having a trehalose structure as an end unit from one or more reducing partial starch hydrolysates with a glucose polymerization degree of at least three; and a trehalose-releasing enzyme, as disclosed in Japanese Patent Kokai No. 213,283/95, which specifically hydrolyzes the bonding between the part of a trehalose structure and the resting part of a non-reducing saccharide having a trehalose structure as an end unit and a glucose polymerization degree of at least three. Journal of Chemical Physics, Vol. 77, No. 5, pp. 2,330-2,335 (1982) reported the structure of crystalline trehalose dihydrate which has an orthorhombic structure as shown in FIG. 1, and has axes having different lengths and crossings at right angles, i.e., it has the a, b, and c axes, and which more elongates to the direction of the c axis than to the b axis, resulting in growth of an easily fragile slender shape of crystal. In fact, commercially available crystalline trehalose dihydrate has a rather slender shape as shown in FIG. 2, a microscopic photograph, where the proportion of the length to the direction of the c axis (the length to the direction of the c axis is abbreviated as the c axis throughout the specification, unless specified otherwise) to that of the b axis (the length to the direction of the b axis is abbreviated as the b axis throughout the specification, unless specified otherwise) is about 3.5 to about 5.5 folds and the c axis is about 2 mm at the longest. Commercially available crystalline trehalose dihydrate has a proportion of length to the direction of the c axis to that of the a axis (the length to the direction of the a axis is abbreviated as the a axis throughout the specification, unless specified otherwise) is about 8 to about 12 folds. The aforesaid conventional crystalline trehalose dihydrate is generally too large in surface area, resulting in the following drawbacks: It is not easily separated from molasses in the separation steps; it needs a relatively-large amount of drying energy; and it is easily fragile during the steps of drying and sieving. Moreover, conventional slender shape of crystalline trehalose dihydrate could not hardly process candy fluff using commercially available machines therefor and hardly be used to process alcoholic beverages with fruits such as ume brandy because the crystal easily dissolves in water. Unlike conventional crystalline trehalose dihydrate, greatly expected is the establishment of a crystalline trehalose dihydrate that can be easily separated and dried in its processing, free of fracture during the steps of drying and sieving, and arbitrarily used to produce candy fluffs and alcoholic beverages with fruits.
The present invention aims to establish crystalline trehalose dihydrate, that can be easily separated and dried in its processing and free of fracture during the steps of drying and sieving, and to provide its process and uses as compositions containing the crystal.
To overcome the above object, the present inventors eagerly studied on the relationship between the lengths of the axes c and b of a crystalline trehalose dihydrate, and found the conditions for growing such a crystal. As a result, they found that the above object is attained by growing a crystalline trehalose dihydrate having an elongated crystal structure with a proportion of the c axis to the b axis of less than 2.0, or preferably one having a proportion of the c axis to the b axis of less than 2.0, where the c axis is at least 3 mm.
The present inventors found that a crystalline trehalose dihydrate, that can be easily separated and dried in its processing and free of fracture during the drying and sieving steps, can be obtained by placing a supersaturated aqueous trehalose solution with a trehalose content of at least about 98 w/w % (the wording xe2x80x9cw/w %xe2x80x9d is abbreviated as xe2x80x9c%xe2x80x9d throughout the specification, unless specified otherwise), on a dry solid basis (d.s.b.) in terms of its anhydrous form, and coexisting crystalline trehalose dihydrate as a seed crystal while controlling the supersaturation degree to a level of less than 1.15 to grow the crystal; and they accomplished this invention by establishing the process and uses of the present crystalline trehalose dihydrate. The present invention achieves a crystalline trehalose dihydrate having an elongated crystalline structure with a proportion of the c axis to the b axis of less than 2.0, and reaches the above object by establishing the process and uses as compositions containing the crystal.